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# contour.c.fix.991130
--- contour.c.ORIG Thu Dec 3 22:23:46 1998
+++ contour.c Wed Dec 1 21:07:24 1999
@@ -536,8 +536,8 @@
struct edge_struct **p_edges; /* list of edges output */
{
int i, j, grid_x_max = iso_lines->p_count;
- struct edge_struct *p_edge1, *p_edge2, *edge0, *edge1, *edge2, *pe_tail,
- *pe_tail1, *pe_tail2, *pe_temp;
+ struct edge_struct *p_edge1, *p_edge2, *edge0, *edge1, *edge2,
+ *pe_tail, *pe_tail2, *pe_temp;
struct poly_struct *pp_tail, *lower_tri, *upper_tri;
struct coordinate GPHUGE *p_vrtx1, GPHUGE * p_vrtx2; /* HBB 980308: need to tag *each* of them as GPHUGE! */
@@ -545,14 +545,14 @@
(*p_edges) = pe_tail = NULL;
p_vrtx1 = iso_lines->points; /* first row of vertices */
- p_edge1 = pe_tail1 = NULL; /* clear list of edges */
+ p_edge1 = pe_tail = NULL; /* clear list of edges */
/* Generate edges of first row */
+ /* HBB 19991130: removed effectively unused variable 'pe_tail1' */
for (j = 0; j < grid_x_max - 1; j++)
- add_edge(p_vrtx1 + j, p_vrtx1 + j + 1, &p_edge1, &pe_tail1);
+ add_edge(p_vrtx1 + j, p_vrtx1 + j + 1, &p_edge1, &pe_tail);
(*p_edges) = p_edge1; /* update main list */
- pe_tail = pe_tail1;
/*
@@ -562,10 +562,16 @@
* (pe_tail points on last edge).
*
* Temporary pointers:
- * 1. p_edge2: Top horizontal edge list: ----------------------- 2
- * 2. pe_tail: middle edge list: |\ |\ |\ |\ |\ |\ |
+ * 1. p_edge2: Top horizontal edge list: +-----------------------+ 2
+ * 2. p_tail : end of middle edge list: |\ |\ |\ |\ |\ |\ |
* | \| \| \| \| \| \|
- * 3. p_edge1: Bottom horizontal edge list: ----------------------- 1
+ * 3. p_edge1: Bottom horizontal edge list: +-----------------------+ 1
+ *
+ * pe_tail2 : end of list beginning at p_edge2
+ * pe_temp : position inside list beginning at p_edge1
+ * p_edges : head of the master edge list (part of our output)
+ * p_vrtx1 : start of lower row of input vertices
+ * p_vrtx2 : start of higher row of input vertices
*
* The routine generates two triangle Lower Upper 1
* upper one and lower one: | \ ----
@@ -633,14 +639,21 @@
upper_tri = add_poly(edge0, edge1, edge2, p_polys, &pp_tail);
}
- if ((*p_edges)) { /* Chain new edges to main list. */
- pe_tail->next = p_edge2;
- pe_tail = pe_tail2;
- } else {
- (*p_edges) = p_edge2;
- pe_tail = pe_tail2;
+ if (p_edge2) {
+ /* HBB 19991130 bugfix: if p_edge2 list is empty,
+ * don't change p_edges list! Crashes by access
+ * to NULL pointer pe_tail, the second time through,
+ * otherwise */
+ if ((*p_edges)) { /* Chain new edges to main list. */
+ pe_tail->next = p_edge2;
+ pe_tail = pe_tail2;
+ } else {
+ (*p_edges) = p_edge2;
+ pe_tail = pe_tail2;
+ }
}
+ /* this row finished, move list heads up one row: */
p_edge1 = p_edge2;
p_vrtx1 = p_vrtx2;
}
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